GPS Overview: How Satellite Positioning Works in Modern Vehicles

The Global Positioning System (GPS) is a network of satellites. It tells a
receiver where it is on Earth. The technology is complex. The basic idea is not.
This page explains how GPS works. Then it covers where you will meet it as an
auto technician. Most cars built in the last fifteen years carry a GPS receiver.
Several systems you will be asked to fix depend on it.

How GPS works

GPS is a global radio navigation system. About 31 satellites are active at any
time. Ground stations track them and keep them accurate. The US Department of
Defense built the system for the military. It has been free for civilian use
since the 1980s.

The full name is NAVSTAR GPS. That stands for Navigation System with Timing
and Ranging. The name explains the method. Each satellite carries an atomic
clock. It broadcasts the time and its own position. A receiver on the ground
listens for those signals. Radio waves travel at a known speed. So the delay
between sending and arrival tells the receiver how far away that satellite is.

One satellite puts you somewhere on a sphere. Two narrow that to a circle.
Three give two possible points. One of those is usually out in space, so it can
be ruled out. A fourth satellite corrects the receiver’s own clock. That clock is
cheap and far less accurate than the ones in orbit. This is why a receiver needs
a clear view of at least four satellites.

That matters for diagnosis. Think of a car parked in a metal building or a
multi-storey car park. It may show a poor fix, or none at all. Tall buildings on
both sides of a street do the same thing. This is normal. It is not a fault.

Where you will find GPS in a vehicle

Navigation and infotainment

This is the obvious one. The head unit uses three things: a GPS fix, map data,
and the car’s own speed and steering inputs. Together they place the car on the
map. A customer may say the map jumps or lags. The cause is often the antenna or
its cable. It is less often the head unit itself.

Telematics

Many vehicles carry a telematics control unit, or TCU. This is a separate
module. It has its own GPS receiver and a mobile data connection. It handles
fleet tracking and stolen vehicle recovery. It also handles remote locking and
service reminders sent back to the maker. On a fleet vehicle it may log routes
and driver behaviour too.

Automatic crash notification

Some vehicles send their position to an emergency call centre if the airbags
go off. That only works if two things are true. The GPS receiver needs a current
fix. The mobile connection needs to be live. Check both after any repair that
involved disconnecting the battery. Check them again if you removed trim near an
antenna.

Driver assistance systems

Advanced driver assistance systems (ADAS) are the safety features that steer,
brake, or warn for the driver. Most of the sensing comes from cameras, radar, and
ultrasonic sensors. GPS is not the main input. Some systems do use position data
as a support. One example is slowing the cruise control before a bend the map
already knows about.

ADAS work is now a specialism of its own. ASE stands for the National
Institute for Automotive Service Excellence. It runs an L4 ADAS Specialist
certification test. The test covers how to diagnose, service, and calibrate
radar, camera, and ultrasonic systems. There is no prerequisite test. You do need
three years of hands-on experience before the certificate is issued. An approved
mix of training and experience also counts.

What this means for your training

Many shops still send positioning work away. A technician who understands
these systems can keep it in house. Antenna diagnosis is one example. So is TCU
replacement and coding. So is calibration after a windscreen or bumper repair.
These are billable jobs. They need real knowledge, not a parts swap.

Look for a programme accredited by the ASE Education Foundation. Accredited
means the foundation has checked the school against the industry standard and
approved it. Ask what the course covers on electrical and electronic systems.
Ask whether the school has ADAS calibration equipment on site. Some do and some
do not. It makes a real difference to what you can do in your first week in a
shop.